When I bought my first car, a Triumph Herald convertible, back in 1981, one of the first things I treated it to was a fiberglass hardtop, for more comfort in the winter and to help preserve its original hood. The hardtop came from Smith & Deakin in Worcester, was white with flock spraying inside and shaped like a Herald Coupé roof, except it had rear quarter windows for better visibility. It really looked the part against the Valencia blue paint – and it still does.

Even more remarkably, Smith & Deakin is still in business, offering a range of hardtops for classic cars. As well as the Herald/Vitesse one (£395) you can buy a top for a Jaguar E-type, Mazda MX5, MGA/B/C/Spridget/F, Sunbeam Alpine/Tiger and Triumph TR2-3. And they’re not the only ones: Honeybourne Mouldings in Warwickshire offers hardtops for classics including E-type, Sprites, MGA/B/F, Midgets, Sunbeam Tiger/Alpine III-V and Triumphs TR2-6, Spitfires and Herald/Vitesse, with prices ranging from £290 for the Midgets to £625 for the MGF. Several other fiberglass moulders in the UK offer hardtops for more recent cars, including nascent classics like Mazda MX-5s and Porsche Boxsters. In continental Europe, a Wiesmann hardtop is the ultimate and is available for a wide range of cars from Fiat Barchetta to Mercedes CLK (and Jaguar XK8).

The most important consideration when looking at a hardtop is how well, and how easily, it fits. This is where Original Equipment tops usually score highest over aftermarket tops, which are unlikely to have had the same development budget and attention to detail spent on them. Certainly the fixings for my Herald hardtop left a lot to be desired: the simple angle brackets at the front were just OK, though you had to be careful not to overtighten them or it would crack the fiberglass, but we had to change the angle brackets in the rear corners, as they just weren’t up to the job. Triangulating the bracket made all the difference. When you’re buying, the fitting kit is more important than the top itself: if the top doesn’t fit properly, you might as well throw it away.

This is an equally important consideration with modern cars, especially if you are buying a secondhand top for a car that wasn’t equipped with it when new. The BMW Z3, for example, came with a significant amount of extra fittings when a hardtop was specified, including the switch for the heated rear window, and even had its own handbook: if you buy one secondhand, make sure you get everything or you could find yourself spending a great deal more money with your BMW agent before you have a top that fits and works as it should.

Storing the hardtop when off is the next consideration: hardtop stands are available for those who have space for them, while others hang them from the garage roof or lean them against a wall, but they do take up a lot of room and are easily damaged.

SteelSteel hardtops are the ultimate in terms of rigidity and therefore insulation and comfort. Classic convertible manufacturers generally offered steel hardtops as original equipment or extra cost options, from the Triumph TR2 in 1955 onwards and, back then, they represented a world of difference over the simple convertible roof. Bolted securely in place, a steel hardtop will actually stiffen the bodyshell, reducing scuttle shake and improving cornering feel, as well as reducing wind resistance and often increasing interior space. No wonder many racing sports cars, especially TRs and E-types, run with fixed hardtops, though usually of aluminum for lightness.

With a steel hardtop firmly secured in place, an open car can feel as civilized as a fixed-head coupé in inclement weather. Triumph made a particularly fine one for the Stag, secured at five points with simple lever controls so easy to remove in a couple of minutes, but very solid when attached and automatically connected to the heated rear window wiring. Unfortunately, as with all steel hardtops for larger cars, it is extremely heavy and almost impossible for one person to remove or refit, certainly without scratching the paintwork. Owners who live alone must resort to Heath Robinson hook and pulley systems attached to the garage roof to raise and lower the top. Steel hardtops are also, of course, liable to rust, so check carefully when buying secondhand.

AluminumBeing lighter than steel, an aluminum hardtop is much easier to manhandle on and off than a steel one and also reduces the tendency of a heavy steel hardtop to raise the car’s center of gravity when cornering. Several manufacturers from Sunbeam in the 1950s to Lotus today have chosen aluminum for their OE hardtops, but it is inevitably more costly than fiberglass or steel.

‘New’ materialsDue to cost and the relatively small weight benefit over fiberglass, carbon fibre or Kevlar hardtops are rare, though we have seen them advertised for Honda S2000 at just under £1000. Transparent polycarbonate is another wacky material that has been used for hardtops, though it’s only really for exhibitionists who are prepared to be frazzled when the sun comes out, unless you have very powerful air conditioning. It tends to be used only for targa-top cars, just for a lift-out panel – one is available for the Bugatti Veyron Grand Sport…

And this brings us to the next trend against open cars: as aircon gets more effective and less power-sapping, manufacturers are increasingly fitting large fixed (or opening) glass roofs that can give an open-car feel without the wind buffeting and pollution, and can be ‘closed’ with a simple blind when preferred (soon to be superceded by in-glass transparency control technology). Available in cars from Fiat 500 up and with no impact on storage space or expensive mechanisms, glass roofs herald another trend away from open cars like we saw in the 1970s. Glass is preferred but polycarbonate may be used too; the largest polycarbonate roof panel currently (1.2 square meters) is on the Smart fortwo and is made by Webasto in Germany.

Retractable Hardtops (RHT)Detachable hardtops are, generally speaking, great when they’re on, but a real pain when they’re not. They take up a lot of storage space, it can be difficult to keep the headlining clean in storage, they are bulky and awkward to take on and off, many requiring at least two people to lift them on and off safely – and if you don’t have a hood, you run the risk of getting soaked if it starts raining. Remarkably, quite a few cars were sold in the past with detachable hardtops and no hood, Triumph Spitfires being one example. It does make for a neater interior and if you’re never going to take the top off, or only when perfect weather is guaranteed, it’s not such a hardship.

But since the 1920s, inventors have been working on the challenge of making a retractable hardtop, giving all the advantages of a closed car in inclement weather – good insulation against rain, cold and sound, clear rear visibility etc – with the benefit of fresh air when you want it. The penalties, of course, are cost, mechanical complexity and an inevitable encroachment on luggage space.

The first successful retractable hardtop was conceived in USA as early as 1922 and fitted to a Hudson Coupe. The first powered production retractable hardtop was on Georges Paulin’s magnificent Peugeot 402 Eclipse Décapotable, a car we’ve all seen in recent years on Peugeot’s TV adverts for its new Coupé-Cabriolets. Cars like the 1957 Ford Skyliner from USA scaled up the concept and 48,394 were sold, though it was neither cheap nor particularly reliable with 10 relays, 10 limit switches, four lock motors, three drive motors, eight circuit breakers and 190 metres of wiring: Ford deleted the model in 1959.

It is only in recent years, as cars have become more complex anyway, that the extra cost of the technology involved has become justifiable. Advances in door and window sealing, electronics and hydraulics, plus the miniaturization, reliability and lower cost of many components, have also made it easier to fit folding hardtops to smaller cars without losing all luggage space, and to achieve consistent accuracy of fit that is vital for effective sealing. Since 2000, over 25 new retractable hardtop cars have been launched, from the tiny Daihatsu Copen to Mercedes-Benz SLKs. The VW Eos retractable hardtop even has an opening sunroof option. Manufacturers argue that this market sector will grow – open-top cars are currently selling at 1 million a year but they claim that the RHT trend will boost this to 1.4 million.